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coin flipped?

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by Hano » Thu Dec 06, 2007 8:28 pm
If a certain coin is flipped, the probability that the coin will land heads is 1/2. If the coin is flipped 5 times, what is the probability that it will land heads up on the first 3 flips and not on the last 2 flips?
A. 3/5
B. 1/2
C. 1/5
D. 1/8
E. 1/32
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by camitava » Thu Dec 06, 2007 9:11 pm
IMO E i.e. 1/32. What do u think guys?
Correct me If I am wrong


Regards,

Amitava
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by Hano » Thu Dec 06, 2007 9:40 pm
please explain!!!
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by camitava » Fri Dec 07, 2007 1:04 am
Hano, for the first three toss, we have to get head. So probability becomes = 1/8. But for the last two toss, we have to get tail. For the last two toss, the probability will be = 1/4. So the total probability will be = 1/8 * 1/4 = 1/32. Get me, Hano?
Correct me If I am wrong


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Amitava
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by Hano » Fri Dec 07, 2007 8:48 pm
got it, thanks
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by jayhawk2001 » Sat Dec 08, 2007 9:37 am
I get 1/32 as well

We are asked to find probability of HHHTT from the 32 possible
combinations. So, 1/32
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Re: coin flipped?

by Brent@GMATPrepNow » Wed Jan 22, 2020 4:32 pm
Hano wrote: ↑
Thu Dec 06, 2007 8:28 pm
 If a certain coin is flipped, the probability that the coin will land heads is 1/2. If the coin is flipped 5 times, what is the probability that it will land heads up on the first 3 flips and not on the last 2 flips?
A. 3/5
B. 1/2
C. 1/5
D. 1/8
E. 1/32
We want P(heads on 1st AND heads on 2nd AND heads on 3rd AND tails on 4th AND tails on 5th)
= P(heads on 1st) x P(heads on 2nd) x P(heads on 3rd) x P(tails on 4th) x P(tails on 5th)
= 1/2 x 1/2 x 1/2 x 1/2 x 1/2
= 1/32

Answer: E

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
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